Imaging methods for displaying examination objects, in particular for determining material properties, the material arrangement and expansion or suchlike are widespread in particular in terms of their medical application.
The image data of various known medical examination facilities allows for different conclusions. While x-ray-based image data allows for statements to be made about the attenuation coefficients of the imaged examination object, magnetic resonance tomography enables knowledge to be obtained about the proton density or the density of the respectively excited cores, relaxation parameters and other variables. Positron emission tomography by contrast enables functional imaging, without reaching the local resolution of the magnetic resonance tomography for instance. There is therefore the need for combined medical examination facilities, which allow for the receiving of image data from a number of examination facilities, in order ultimately to acquire fused image data. Improved information can then be derived from this fused image data for diagnosis purposes in particular than when taking just singular image data into account, in other words image data from a single examination facility.
Magnetic resonance tomography (MRT) is an imaging method, which allows for the high resolution generation of sectional images of living organisms, such as humans. The patient is positioned in a homogeneous magnetic field B0. With gradient coils, the outer magnetic field in the FOV (field of view) is modified such that a body layer is selected on the one hand and a local encoding of the generated MR signals takes place on the other hand. With the subsequent reconstruction of the MR signals for instance by way of Fourier transformation, an image of the selected layer is produced, which is used for medical diagnostics. The generation and detection of MR signals takes place with a high frequency system, which includes a transmit antenna, which radiates HF excitation pulses into the patient, and a receive antenna, which detects the emitted HF resonance signals and forwards the same for image reconstruction purposes. By selecting a suitable pulse sequence, such as a spin echo sequence or a gradient echo sequence, and the sequence parameters associated therewith, the contrast of MR images can be varied considerably depending on the diagnostic task description. The MRT images body structures and accordingly represents a structural imaging method.
Positron emission tomography (PET) is a widespread method for functional imaging. During an examination, a weak radioactive substance is administered to an examination person, the distribution of which in the organism is made visible by way of PET. As a result, biochemical and physiological functions of the organism can be mapped. Molecules are used here as radiopharmaceuticals, said molecules being marked with a radionuclide which emits the positrons. The high-energy photons produced during the annihilation of the positron with an electron in the body of the examined person, which are emitted at an angle of 180° relative to one another, are detected with a plurality of detectors arranged in an annular fashion about the examination person. Only coincidental events, which were recorded with two opposing detectors, are evaluated in each instance. The spatial distribution of the radiopharmaceutical in the inside of the body is concluded from the registered coincidental decay events and a series of sectional images is calculated. The image reconstruction can take place in such cases with a filtered back projection or an iteration method, wherein the spatial resolution generally remains inferior to the resolution of conventional computed tomography (CT) or magnetic resonance tomography systems.